The present invention relates in general to engine brake retarders of the compression release type. More particularly, the present invention pertains to an improved hydraulic circuit solenoid valve which combines solenoid and control valve functions into a single component.
Engine brake retarders of the compression release type are believed to be well known in the art. These devices may be referred to as an engine brake or engine retarder, but regardless of the name, the theory of operation is basically the same. In general, such engine retarders are designed to control the motion of a slave piston which opens the exhaust valves of an internal combustion engine cylinder near the end of the compression stroke. As a result, the work done in compressing the intake air is not recovered during the expansion stroke, but rather is dissipated through the exhaust (and cooling) systems of the engine.
One current style of engine retarder is represented by the Cummins Engine C Brake which is offered by Cummins Engine Company, Inc., of Columbus, Ind. The C Brake is a highly efficient engine retarder which is used for reducing vehicle speed. The theory of operation, which is similar in certain respects to other engine retarder designs, uses a hydraulic circuit that opens the exhaust valve(s) near the end of the compression stroke. When the C Brake is activated and the vehicle is moving, the engine produces a compression braking effect.
The C Brake uses one solenoid valve for each pair of engine cylinders in combination with two control valves, one for each cylinder. These components are assembled into a housing which is mounted directly on top of the rocker housing. When the solenoid valve is energized, engine oil enters the C Brake system through the rocker arm pedestal. As engine oil flows into the C Brake, the control valve is forced in an upward direction. A minimum of 18 psi is required to open this control valve. When the cross drilling in the control valve is aligned with the high pressure drilling, oil flows past a check ball into the master piston and slave piston high pressure circuit. This entering oil added pressure causes the master piston and slave piston to move in a downward direction.
As the injector push rod begins its upward travel, the injector rocker arm adjusting screw begins to force the master piston in an upward direction. This action closes the control valve check ball and as a result, oil is then trapped in the high pressure circuit. The continuing upward movement of the injector push rod increases the oil pressure and ultimately forces the slave piston to travel in a downward direction. With this advancing travel in a downward direction by the slave piston, it applies force to the cross head of the exhaust valves, forcing those valves to open. The opening of the exhaust valves allows compressed air to escape from the corresponding cylinder and thus a compression braking cycle has been completed. At the completion of this cycle, the injector push rod and master piston travel in a downward direction and this allows the oil pressure in the high pressure circuit to return to normal. Immediately, the slave piston moves in an upward direction, allowing the exhaust valves to close. Any leakage from the high pressure circuit is made up at this time by engine oil which enters through the solenoid valve and check valve within the control valve.
When the solenoid is de-energized, oil in the C Brake is returned to the engine. This allows the C Brake to be returned to its de-activated position and the master and slave pistons are retracted by spring pressure. As a result, these pistons are moved out of the way of normal engine operation.
One of the design realities with this type of engine retarder is the use of a control valve, one for each cylinder, which uses a control spring. Such springs have had, on occasion, reliability concerns and the elimination of the control valve springs would obviously avoid such concerns. Another design reality is the size of the control valve and its required travel distance. This also influences the size of the assembly housing which is required. If the control valve function can be combined as part of a new solenoid valve design, then the size of the engine retarder can be reduced. The present invention provides such an improved design.
While the Cummins Engine C Brake design represents one engine retarder arrangement, there are other configurations which deserve consideration when reviewing the complexity of engine retarder systems. One example of another system which uses a solenoid in combination with a control valve is disclosed in U.S. Pat. No. 4,996,957 which issued Mar. 5, 1991, to Meistrick. The disclosed device of Meistrick includes a first flow network for the delivery of oil at low pressure to a solenoid valve and from there to a control valve. Oil also fills the chambers of a slave cylinder and master cylinder. During a retarding event, the master piston moves upwardly in the cylinder in response to the motion of a push tube, creating a high pressure force which in turn forces the slave piston to move in a downward direction. The corresponding movement of the slave piston in a downward direction opens the exhaust valves near the end of the compression stroke of the engine.
As will be appreciated, the Meistrick device includes a number of components and controls including a specific control valve for the high pressure fluid circuit. There are also two flows which have to be managed by the controls and valves, including a low pressure oil delivery flow (and fill) and a high pressure, valve-opening flow. The result of this complexity is a significant size requirement and thus a need for a significant area or space in which to mount all of the required hardware and all in the vicinity of the cylinder exhaust valves.
It would be an improvement to the complexity of designs such as that described in the Meistrick patent if a single solenoid component could be designed to combine both the solenoid and control valve functions into one item. Ideally this would permit a smaller package size for the engine brake. Added benefits of such an improvement would be a reduction in the machining required to create the now-required control valve and solenoid drillings. If the currently used control valve can be eliminated by a combined solenoid design, then the now-required control valve spring could also be eliminated. Since the control valve springs have historically presented certain problems with regard to reliability, elimination of this spring would represent a substantial benefit to the engine brake in terms of improved reliability.
The present invention provides the aforementioned type of design improvement by a novel and unobvious solenoid valve which combines the solenoid and control valve functions into a single component. The result is a smaller package size and a design which handles both the low pressure flows as well as the high pressure flows.
In addition to what is disclosed in the Meistrick patent, there have been other solenoid and control valve arrangements invented over the years. The following listed patent references are believed to be a representative sampling of such earlier solenoid and control valve designs.
______________________________________ PATENT NO. PATENTEE ISSUE DATE ______________________________________ 2,944,565 Dahl July 12, 1960 3,220,392 Cummins Nov. 30, 1965 3,332,405 Haviland July 25, 1967 3,921,666 Leiber Nov. 25, 1975 4,251,051 Quenneville et al. Feb. 17, 1981 4,460,015 Burt et al. July 17, 1984 4,844,119 Martinic July 4, 1989 ______________________________________
While the handling of either low pressure flows or high pressure flows may be possible with one or more of the devices disclosed in the above list, nothing is disclosed which handles both by means of a single solenoid component as is provided by the present invention. For example, the Quenneville, et al., patent describes a solenoid which is used for controlling low pressure oil to an engine brake. In the Meistrick design the control function focuses on the high pressure circuit and not the low pressure supply side.